Stabilized polyamides containing cupric acetate, cupric chloride and 2-mercaptobenzothiazole



United States Patent M This invention relates to a nylon composition suitable for use under conditions of high temperature and high humidity. More particularly, this invention relates to a nylon composition that may be used under conditions of high temperature, and high humidity in the presence of and in contact with food for human consumption with- 1 out adversely affecting the properties of food. Specifically, this invention relates to a nylon composition that may be used in contact with hot beverages without degrading the nylon and without adversely affecting the beverage.

Over a period of years considerable research attention has been directed to developing an effective stabilization system for nylon under conditions of high humidity and relatively high temperature (about 100 C.). Although some success has been achieved in this area, prior to this invention no stabilized nylon composition was available that could be used in contact with hot food for human consumption, for the materials added to the nylon to stabilize it against hydrolytic and oxidative degradation were quite toxic.

It is an object of this invention to provide a nylon I composition that is stable under conditions of high humidity and high temperature, and which may be used in contact with hot food for human consumption without adversely affecting the properties of the food. It is a further object of this invention to produce a nylon composition which maybe molded or extruded to form a where R is hydrogen or a monovalent hydrocarbon radical having 1 to 10 carbon atoms as an integral part of the resin polymer chains. The average number of carbon atoms separating the amide groups is at least. two. These polymers are capable of being formed into filaments in which the structural elements are oriented in the direction of the filament axis. The nylons in the composition of this invention may be prepared, for example, by the condensation reaction of hcxamethylene diamine and adipic acid or sebacic acid or by polymerizing epsilon caprolactam in the presence of a diamine. In general, the nylons should have an inherent viscosity of between about 0.75 and 1.70, where inherent viscosity is defined as 1 reL/C, n rel. being the efllux time of a 0.5 g./ 100 cc. solution of the polymer in 98% meta-cresol divided by the effl-ux time, of 98% meta-cresol, the efflux Patented Mar. 7, 1967 concentration in g./ 100 cc. The nylons in the compo.- sition of this invention are readily processable by injection molding or by extrusion to form useful articles.

The nylons in the composition of this invention must have an excess of amine end groups over carboxyl end groups. As a convenient method of describing the quantity of amine or carboxyl groups, the art has described the excess in terms of the number of gram equivalents of amine groups that are present in excess of the number of carboxyl groups per 10 grams of polymer. See Journal of American Chemical Society, vol. 69, pp. 635- 638 (1947). In the nylons used in the present invention, the excess must be within the range of about20 to 140 and preferably 40 to 100 gram equivalents of amine groups in excess of the number of equivalents of carboxyl groups per 10 grams of polymer.

The concentration of carboxyl end groups in polyamide resin is determined as follows: 'a solution of 1 N NaOH in aqueous methanol is diluted to 0.1 N concentration with benzyl alcohol and standardized against pure benzoic acid with phenolphthalein indicator. About 3 grams ofthe polyamide is weighed and dissolved in 75 ml. benzyl alcohol at 185200 C. The hot solution is titrated to a phenolphthalein end point with 0.1 N NaOH described above.

A blank is titrated'in the same way with 75 ml. of benzyl alcohol. The net titer is the sample titer less the blank titer.

net titerXN NaOHXlO a sample Wt., g. l0

The concentration of amine end groups in polyamide resin is determined as follows: a solution of perchloric acid approximately 0.05 N in methanol is prepared and standardized by titration with 0.1 N NaOH in methanol to the phenolphthalein end point. About 3 grams of the polyamide is weighed and dissolved in 75 ml. of redis- =carboxyl equivalents/10 g.

tilled meta-cresol. Ten ml. of methanol is added. The

pH of the stirred solution is measured by means of an electrode pair, glass and silver-silver chloride, 'while standardized perchloric acid solution is introduced by a buret whose tip is immersed in the polyamide solution. A plot of acid volume on the abscissa vs. pH on the ordinate is made. The equivalence point is taken as the midpoint of the straight portion of the most nearly vertical part of the curve.

The composition of this invention contains between about 0.02 and about 0.08 percent by weight of the composition of cupric chloride, between about 0.02 and about 0. 08 percent by weight of the composition of cupric acetate, and about 0.05 to 0.5 percent by weight of the composition Z-mercaptobenzothiazole or its copper salt, i;e.,

' the chemical compounds corresponding to theformula:

C-SH, or

' during'polymerization, or prior to polymerization, for the stabilizers are relatively non-volatile.

The 2-mercaptobenzothiazole or its copper salt may be added as a solid or in solution, e.'g.-, an ethanol solution. Other additives 1 such as dyes, pigments, and other stabilizers may also be times for the solution and solvent being measured inthe 1 same viscosity pipet at the same temperature, and C being present so Ion-g as they do not affect the basic characteristics of the composition.

In the following examples all. parts and percentages are in parts by weight unless otherwise specified.

3 EXAMPLE 1 One hundred and forty-three pounds of a 50.61% aqueous solution of hexa methylene diam-monium adipate was concentrated by vacuum distillation, and the result- The results show that the composition of this invention is very stable and not subject to extraction to an appreciable extent by any of the above common solvents.

I claim:

ing solution was transferred to a jacketed, stirred auto- 5 hydrolysle and ,oxldaheh reslstaht lehg ehalh fiber clave. To the solution was added a solution of 13.6 g. 'g Polymenc amide havmg recumhg amlfle groups each (0.048 wt. percent of polymer) of cupric chloride as an mtegrahpart of the polymer chain havmg 20 to dihydrate and cupric acetate 'monohydrate in about 200 140 gram eqmvalehts of ahhhe groups In excess of the ml. of distilled water, 60.8 g. (0.215 wt. percent of polyh h of carboxyl groups per 106 grams of Polymer mer) of Z-mercaptobenzothiazole in solid form, and 242 talhmg between i h aboufi percent by g. of an 84% aqueuos solution of hexa-methylene diamine Weight of the composltlon cupric p between abolit (dry diamine equivalent to 0.715 wt. percent of polymer). 3 and Fbout Q08 Pfircent y W ight of the compo i- The mixture was subjected to polymerization for approxihon oupne e and between 9 and about mately 5 hours at temperatures up to C and at 0.5 percent by weight of the composition of Z-mercaptopressures from 250 to 0 p.s.i. g. The molten polymer was benzothlazole' extruded with the assistance of inert gas pressure through The corhposlhoh of elahh 1 1h Whleh the hyloh has a flat ribbon die, quenched, and cut into pieces suitable an Inherent vlscoshy of between h for use in an injection molding machine. The product The eomposltloh of 5 m which the hyloh 15 so obtained was dried to a moisture content of about 0.2 hhear polyhexamethylehe P e' wt. percent. The inherent viscosity (0.5 g. polymer/ 100 The eohhpoeihoh of elahh 1 1h Whleh the hhmher ml. meta-cresol at C.) of this resin was 1.35 deciliters/ of h equlvalehts Per 106 grams of Polymer of afmlhe grain. Analysis showed an excess of amine ends amountgroups In excess of the number he carboxyl groups is ing to 37.7 equivalents per million grams of polymer. tween and Test specimens were made from this resin by injection 25 A eomposlheh Mable for use h the preparahoh of molding. Specimens were exposed to boiling water for molded pares which e e essehhahy of (1) nylon long periods and others were subjected to the accelerated Polymer havlng l'ecufrlng amide groups of the formula hydrolysis oxidation test. The accelerated hydrolysis C oxidation test consists of exposure under water in an autot P clave containing air at 140-144 C. for 64 hours followed 30 by exposure to air saturated with water vapor at 140- 144" C. for 16 hours. All specimens were conditioned to relative humidity before testing. The results are compared below with similarly prepared resins of different composition.

where R is selected from the group consisting of hydrogen and monovalent hydrocarbon radicals, as integral parts of the main polymer chain, said nylon polymer having an inherent viscosity of between 0.75 and 1.70, said nylon having per 10 grams of polymer between 20 and Gram equiv. of amine groups in Tensile Impact excess of the Sample Test (ft.-lb./in. Inherent Viscosity number of grams equiv. of carboxyl groups Initial Properties 166 1. 35 66 Nylon (high NH +0.05% GuGl2+0.05% Cu Accelerated Hydrolysis Oxidati0n. 186 1.07 (OAc)2+0.22% 2-mercaptobenzothiazole. 720 hours Boiling Water 147 1. 27 1,500 hours Boiling Water" 181 1. 21 Initial Properties 130 1. 35 66 Nylon (high NH +02% 4,4butylidene-bis Accelerated Hydrolysis Ox 133 1. 11 (6 t-butyl meta-cres0l). 720 hours Boiling Water 127 1. 30 1,500 hours Boiling Wate 128 1. 14 initial Progerrltieis d 144 1. 35 cce erate y rolysis Oxi ation 15 1.05 66 Nylon (high NHZ) addltlve5 72 hours Boiling Water 139 l. 29 1,500 hours Boiling Water 151 1. 20

EXAMPLE II A 66 nylon polymer with excess amine ends of 52 equivalents/1X10 grams of polymer, 0.05% each of cupric acetate and cupric chloride, and 0.22% of 2-mer- ,captobenzothiazole was prepared as described in Example I. The granules which were approximately x x inch cubes were subjected to extraction tests by boiling 3 0 grams of the nylon in 300 milliliters of solvent in a 500 milliliter round-bottom flask equipped with a reflux condenser.

gram equivalents of amine end groups in excess of the number of carboxyl end groups, (2) between about 0.02 and about 0.08 percent by weight of the composition cupric chloride, (3) between about 0. 02 and about 0.08 percent by weight of the composition cupric acetate, and (4) between about 0.05 and about 0.5 percent by weight of the composition of 2- mercaptobenzothiazole.

6. The composiiton of claim 5 in which the nylon is linear polyhexamethylene adipamide.

7. The composition of claim 6 in which the number of equivalents per 10 grams of polymer of amine end groups in excess of the number of carboxyl groups is between 40 and 100.

References Cited by the Examiner FOREIGN PATENTS 2/1962 Great Britain. 9/1963 Japan. 

1. A HYDROLYSIS AND OXIDATION RESISTANT LONG CHAIN FIBER FORMING POLYMERIC AMIDE HAVING RECURRING AMIDE GROUPS AS AN INTEGRAL PART OF THE POLYMER CHAIN HAVING 20 TO 140 GRAM EQUIVALENTS OF AMINE GROUPS IN EXCESS OF THE NUMBER OF CARBOXYL GROUPS PER 10**6 GRAMS OF POLYMER CONTAINING BETWEEN ABOUT 0.02 AND ABOUT 0.08 PERCENT BY WEIGHT OF THE COMPOSITION CUPRIC CHLORIDE, BETWEEN ABOUT 0.02 AND ABOUT 0.08 PERCENT BY WEIGHT OF THE COMPOSITION CUPRIC ACETATE, AND BETWEEN ABOUT 0.05 AND ABOUT 0.5 PERCENT BY WEIGHT OF THE COMPOSITION OF 2-MERCAPTOBENZOTHIAZOLE. 